This invention relates to a vehicle heating, ventilation and air conditioning (HVAC) system having an air quality sensor and an inlet air control valve, and more particularly to an improved method of operating the inlet air control valve.
Vehicle HVAC systems commonly include an inlet air controller such as a movable valve or shutter (referred to herein simply as an inlet air valve) that is positioned to control what proportion of the inlet air is drawn from inside and outside the vehicle cabin. In a typical application, a system controller positions the air inlet valve to optimize system efficiency and occupant comfort, and the occupant is permitted to override the normal control when full cabin air recirculation or full outside air is desired. For example, cabin air recirculation may be used to limit the intrusion of polluted air when driving in congested traffic, and full outside air may be used to purge the cabin of smoke or odors. However, the average driver frequently fails to manually position the inlet air valve as recommended, and sometimes polluted air has already entered the cabin by the time the driver switches to cabin air recirculation. For these reasons, the trend is to equip vehicle HVAC systems with a filtering system and one or more air quality sensors; the filtering system filters particulates and odors from the inlet air, and the inlet air valve is automatically positioned based on the air quality sensor to minimize the amount of polluted air entering the inlet air stream. See, for example, the U.S. Pat. No. 5,725,425 to Rump et al., issued on Mar. 10, 1998, and incorporated by reference herein.
A problem that occurs with automated positioning of the inlet air valve based on air quality sensing is that the HVAC system can be repeatedly cycled between the outside air and recirculation modes, particularly when the vehicle is operated in congested city traffic. Each opening and closing of the air inlet valve changes the HVAC noise level in the cabin, and the changing noise level can be annoying to the vehicle occupants. Accordingly, what is needed is an improved method of operating the air inlet valve in response to detected inlet air quality that provides the improved cabin air quality in a way that is less perceptible to the vehicle occupants.
The present invention is directed to an improved method for controlling an inlet air valve in a vehicle HVAC system including an air quality sensor in an outside air inlet passage, wherein the air inlet valve is immediately closed to provide cabin air recirculation when the sensor detects the presence of polluted air, and is thereafter re-opened at a determined rate when the outside air is no longer polluted. In a preferred embodiment, the air quality sensor output quantifies the pollution level of the inlet air, and the opening rate of the air inlet valve is determined based on the detected level. Following a high level of detected air pollution, the valve is re-opened at a relatively slow rate, and following a low level of detected air pollution, the valve is re-opened at a relatively fast rate.